Solid Earth Tides in Space Geodetic Techniques

- Wu Bin (Instiute of Geodesy and Geophysics, Chinese Academy of Science, Wuhan, CHINA)

- Trevor Baker (POL, Bidston)
- Yoichi Fukuda(Kyoto Univ., Kyoto)
- Ruediger Haas (OSO, Onsala)
- P.M. Mathews (Univ. Madras, Chennai)
- Juergen Mueller (TUM, Muenchen)
- Hans-Georg Scherneck (Chalmers Univ. of Techn., Gueteborg)
- Oleg Titov (AUSLIG, Canberra)
- Shailen Desai (JPL, Pasadena)
- Robert Weber (TUW, Wien)
- Harald Schuh (TUW, Wien)
- C.K. Shum (OSU, Ohio)
**Spiros Pagiatakis (York University, Tronto)**

The correspondents of WG6 in the last term are considered to continue working in the new term. There are seven new correspondents who are actively working on the topics of WG6.

The general goal of the WG6 (was already agreed upon in 1997) is to strengthen the links between researchers of the tidal community and those who work in space geodetic techniques in both directions:

- The tidal experts provide precise models for the displacements of observation sites on the Earths crust due to the tides and for the tidal variations to the gravitational field of the Earth.

- The space geodetic techniques are used to validate and possibly to improve the tidal models, e.g. the tidal parameters.

### Terms of Reference (ToR)

- Cooperation with the analysis coordinators of the new IAG international
services, e.g. IGS, IVS, ILRS, IDS, ... and the Working Groups which exist
within these services,

- Comparison of tidal parameters obtained from the different techniques,

- Comparison of results obtained by space geodetic techniques and
ground-based tidal measurements,

- Exploring new satellites measurements (CHAMP and GRACE) for Earth tides,

- Using GPS and ground-based gravimeter to study regional ocean tides.

### For further information contact:

Dr. Wu, Bin

Chairperson ETC Working Group 6

Instiute of Geodesy and Geophysics

Chinese Academy of Science

54 Xu-dong Road, Wuhan, CHINA

Phone:+86-27-86783918

Fax: +86-27-86783841

e-mail: bwu@asch.whigg.ac.cn

## Report of the Working Group 6 (1997-2000)

- Status August 28, 2000 -

by Harald Schuh

University of Technology Wien

Austria

e-mail: hschuh@luna.tuwien.ac.at

### |||||1. Introduction

The IAG/ETC Working Group 6 'Solid Earth tides in space geodetic techniques' was established at the XIIIth International Symposium on Earth Tides, Brussels, July 1997. The general goal of the WG is to strengthen the links between researchers of the tidal community and those who work in space geodetic techniques. The cooperation shall take place in both directions:

- The tidal experts provide precise models for the displacements of observation sites on the Earth's crust due to the tides and for the tidal variations to the gravitational field of the Earth.
- The space geodetic techniques are used to validate and possibly to improve the tidal models, e.g. the tidal parameters.

For the investigation of the solid Earth tides it is necessary to take also into account other geophysical influences, e.g. those of the oceans, of the atmosphere and of the pole-tide. Thus, oceanic and atmospheric loading, oceanic and atmospheric effects on the geopotential and the pole-tide are regarded by the WG, too.

### Chairman, members and correspondents of WG 6 (status August 2000) are:

Chairman:- Harald Schuh (DGFI, Munchen, since April 2000 TUW, Wien)

- Per-Helge Andersen (NDRE, Kjeller)
- Trevor Baker (POL, Bidston)
- Veronique Dehant (ROB, Brussels)
- Richard Eanes (UTEX, Austin)
- John Gipson (GSFC, Greenbelt) (till 1999)
- Ruediger Haas (OSO, Onsala)
- P.M. Mathews (Univ. Madras, Chennai)
- Jurgen Mueller (TUM, Munchen)
- Richard Ray (GSFC, Greenbelt)
- Hans-Georg Scherneck (Chalmers Univ. of Techn., Goteborg)
- Oleg Titov (Univ., Sanct-Petersburg)

- Duncan C. Agnew (Scripps Inst. of Oceanography, La Jolla)
- Richard Biancale (CNES, Toulouse)
- Karen Bruyninx (ROB, Brusells)
- Robert C. Bostrom (Univ. of Washington, Seattle)
- Jean Chapront (PO, Paris)
- Shailen Desai (JPL, Pasadena)
- Robert Dill (DGFI, Munchen)
- Olivier Francis (ROB, Brusells)
- Pascale Gegout (IPG, Strasbourg)
- Michael Gerstl (DGFI, Munchen)
- Michael B. Heflin (JPL, Pasadena)
- Maria Mareyen (BKG, Potsdam)
- Jurgen Neumeyer (GFZ, Potsdam)
- Ron Noomen (TU, Delft)
- Markuu Poutanen (FGI, Masala)
- Burghard Richter (DGFI, Munchen)
- Judit G. Ries (UTEX, Austin)
- Ernst Schrama (TH Delft)
- Tonie M. VanDam (NOAA, Boulder)
- Peter Varga (GGRI, Sopron)
- John Wahr (Univ. Colorado, Boulder)
- Robert Weber (TUW, Wien)
- Pascal Willis (IGN, Paris)
- Wu Bin (IGG, Wuhan)
- Xi Qinwen (State Seism. Bur., Beijing)
- Kahled Zahran (Univ., Karlsruhe)

The following Terms of Reference (ToR) were agreed upon by the members of WG 6 on Oct., 24th, 1997:### |||||2. Terms of Reference (ToR)

- Extension of the recommendations concerning the tidal influences given in the IERS Conventions (1996) to facilitate their practical use for space geodetic techniques.
- Evaluation and comparison of the potential of different space geodetic techniques to monitor tidal effects and to determine tidal parameters. Techniques such as VLBI, SLR, LLR, GPS and GLONASS, DORIS and PRARE, satellite altimetry will be covered.
- Determination of parameters of the tidal models by space geodetic techniques. This requires a priori corrections due to atmospheric and oceanic influences on the Earth's surface and on the geopotential and precise models for tidal influences on the Earth orientation parameters. The effect of pole-tide has also to be considered. The results will have to be compared and interpreted.

Activities for the 2. Term of Reference started in February 1998 by establishing subgroups which worked on 'supplements' to the IERS Conventions (1996). The goal was to work on an extension of the recommendations concerning the tidal influences given in the IERS Conventions (1996) to facilitate their practical use for space geodetic techniques. Dennis D. McCarthy, editor of the IERS Conventions (1996), was informed.### |||||3. Activities of Working Group 6 from 1997 till 2000

These are the subgroups with the chairpersons given in bold:

Chapter 6 of the IERS Conventions (1996) 'Geopotential'

- Effect of Solid Earth Tides (Eanes, Dehant, Mathews, Ray,...)
- Solid Earth Pole Tide (Andersen, Muller, Schuh, ...)
- Treatment of the Permanent Tide (Mathews, Dehant, Eanes, ...)
- Effect of the Ocean Tide (Ray, Eanes, Baker, Muller, Scherneck, ...)
- Conversion of tidal amplitudes defined according to different conventions (Dehant, Gipson,...)

- Local Site Displacement due to Ocean Loading (Scherneck, Baker, Haas, Muller, ...)
- Effects of the Solid Earth Tides (Dehant, Gipson, Haas, Mathews, Schuh, Titov, ...)
- Rotational Deformation Due to Polar Motion (Andersen, Muller, Schuh)
- Antenna Deformation (Haas, Schuh, Titov, ...)
- Atmospheric Loading (Gipson, Baker, Haas, MacMillan, Scherneck, Schuh, Titov, Vauterin)
- Postglacial Rebound (Ray, Scherneck, ...)

The activities for the 2. and 3. Term of Reference started in summer 1999. New subgroups were established in September 1999, now to evaluate the different space geodetic techniques with respect to their potential to monitor tidal effects and to determine tidal parameters. The subgroups were also open for non-members of the WG. The following questions were addressed by the subgroups:

- Which tidal effects have to be considered in the particular space technique?
- How is the 'permanent tide problem' handled?
- What is the capability of the particular space technique to investigate tidal effects (including oceanic and atmospheric tides) and to determine tidal parameters, e.g. the Love numbers?
- What are the newest results?
- What are the limitations?
- What are the future perspectives?

- WG 6/1 (VLBI): R. Haas, P.-H. Andersen, O. Titov, H. Schuh, P.M. Mathews, V. Dehant
- WG 6/2 (SLR: Wu Bin, R. Eanes, J. Muller, P.-H. Andersen
- WG 6/3 (LLR): J. Muller, J. Chapront, J.G. Ries, J. Williams
- WG 6/4 (GPS/GLONASS): R. Weber, T. van Dam, K. Bruyninx, P.-H. Andersen, T. Baker, M. Rothacher, H.-G. Scherneck
- WG 6/5 (DORIS): R. Biancale, J.G. Ries, P. Willis
- WG 6/6 (Satellite Altimetry): S. D. Desai, R.D. Ray, E.J.O. Schrama

- all space geodetic techniques provide interesting information about tidal effects;
- comparison of the treatment of tidal effects in different software packages revealed considerable discrepancies (e.g. between GPS software packages, between VLBI software packages, between LLR software packages, ...);
- new results for the tidal parameters were obtained for: VLBI: h, l (for individual tides and also for tidal bands: semi-diurnal, diurnal, long-period, second degree and third degree, including phase lags, Haas and Schuh, 1996; Schuh and Haas, 1998) DORIS: h2, k2 (R. Biancale, 2001) LLR: secular tidal acceleration, lunar tidal parameters, h2, l2 (Muller and Tesmer, 2000) SLR: k2, h2 incl. phase lags (for M2, S2, K1, O1) (Wu Bin et al., 2001) GPS: planned Sat. Altimetry: h2 for four tides (Ray et al., 1995), ocean tidal models

- 1st Meeting, during EGS, Nice, April 23rd, 1998
- 2nd Meeting, during IUGG, Birmingham, July 22nd, 1999
- 3rd Meeting, during EGS, Nice, April 26th, 2000

### |||||4. Outlook

The following questions for the future of Working Group 6 were risen:- What else should the WG 6 deliver? (bibliography related to tidal effects and space geodetic techniques?)
- What could be future activities after ETS2000?
- Should WG 6 finish its activities, continue in the present form, continue with different or
- additional goals?

- Cooperation with the analysis coordinators of the new IAG international services, e.g. IGS, IVS, ILRS, IDS, ... and the Working Groups which exist within these services,
- Comparison of tidal parameters obtained from the different techniques,
- Comparison of results obtained by space geodetic techniques and ground-based tidal measurements.

### |||||5. References

- Explanatory Supplement to the IERS Conventions (1996) Chapters 6 and 7, ed. by H. Schuh, DGFI Report 71: http://www.dgfi.badw.de/dgfi/DOC/report71.pdf, 1999.
- Final Report of the IAG/ETC Working Group 6 for the years 1997-2000, ed. by H. Schuh, with contributions by Biancale, Desai et al., Haas et al., Muller et al., Weber et al., Wu Bin et al., BIM, 2001.
- Haas, R. and Schuh, H.: Determination of frequency dependent Love and Shida numbers from VLBI data. Geophys. Res. Lett., Vol. 23, No. 12, 1509-1512, 1996.
- Muller, J. and Tesmer, V.: Investigation of Tidal Effects in LLR. subm. to Journal of Geophysical Research, 2000.
- Ray, R.D. et al.: Geometrical Determination of the Love number h2 at four tidal frequencies. Geophys. Res. Lett., Vol. 22, No. 16, 2175-2178, 1995.
- Schuh, H. and Haas, R.: Earth Tides in VLBI Observations. Proc. of the 13th International Symp. on Earth Tides, Brussels, 1997, ed. by B. Ducarme and P. Paquet, Serie Geophysique, Obs. Royal de Belgique, 101-110, 1998

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